Components of other intangible assets subject to amortization (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Core Deposits, Gross	$ 3,000
Finite-Lived Customer Relationships, Gross	4,000
Gross Amount	94,908	100,786
Finite Lived Intangible Assets Accumulated Amortization	41,778	42,945
Finite-Lived Intangible Assets, Net	53,130	57,841
Core Deposits Member
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Core Deposits, Gross	77,885	80,591
Finite Lived Intangible Assets Accumulated Amortization	39,571	38,199
Finite-Lived Intangible Assets, Net	38,314	42,392
Customer Relationships Member
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Customer Relationships, Gross	16,835	19,953
Finite Lived Intangible Assets Accumulated Amortization	2,111	4,643
Finite-Lived Intangible Assets, Net	14,724	15,310
Other Intangible Assets Member
Finite-Lived Intangible Assets [Line Items]
Other Finite-Lived Intangible Assets, Gross	188	242
Finite Lived Intangible Assets Accumulated Amortization	96	103
Finite-Lived Intangible Assets, Net	$ 92	$ 139